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R McChesney

Publications and source records attributed to R McChesney.

13 recordsLinked to original sources
PubMed2001

Natural limits of pregnancy testing in relation to the expected menstrual period.

CONTEXT: Pregnancy test kits routinely recommend testing "as early as the first day of the missed period." However, a pregnancy cannot be detected before the blastocyst implants. Due to natural variability in the timing of ovulation, implantation does not necessarily occur before the expected onset of next menses. OBJECTIVE: To estimate the maximum screening sensitivity of pregnancy tests when used on the first day of the expected period, taking into account the natural variability of ovulation and implantation. DESIGN AND SETTING: Community-based prospective cohort study conducted in North Carolina between 1982 and 1986. PARTICIPANTS: Two hundred twenty-one healthy women 21 to 42 years of age who were planning to conceive. MAIN OUTCOME MEASURES: Day of implantation, defined by the serial assay of first morning urine samples using an extremely sensitive immunoradiometric assay for human chorionic gonadotropin (hCG), relative to the first day of the missed period, defined as the day on which women expected their next menses to begin, based on self-reported usual cycle length. RESULTS: Data were available for 136 clinical pregnancies conceived during the study, 14 (10%) of which had not yet implanted by the first day of the missed period. The highest possible screening sensitivity for an hCG-based pregnancy test therefore is estimated to be 90% (95% confidence interval [CI], 84%-94%) on the first day of the missed period. By 1 week after the first day of the missed period, the highest possible screening sensitivity is estimated to be 97% (95% CI, 94%-99%). CONCLUSIONS: In this study, using an extremely sensitive assay for hCG, 10% of clinical pregnancies were undetectable on the first day of missed menses. In practice, an even larger percentage of clinical pregnancies may be undetected by current test kits on this day, given their reported assay properties and other practical limitations.

Adult↗
PubMed2000

Video display terminals and miscarriage.

Concern about possible reproductive effects of using video display terminals (VDTs) was stimulated by reports of clusters of adverse pregnancy outcomes among groups of women who used VDTs. Exposure to electromagnetic fields emitted from VDTs was suspected of increasing the risk of miscarriage. Ten epidemiological studies have examined associations between VDT use and miscarriage, most of which were not originally designed to examine this hypothesis and suffer from methodological limitations. We review these studies and present previously unpublished data in support of our conclusion that for most women in modern offices, work with VDTs does not increase their exposure to electromagnetic fields or increase their risk of miscarriage. The miscarriage risk for women who work at high-stress jobs or with older, high-emission VDTs (ELF > 3 mG), however, is still uncertain.

Abortion, Spontaneous↗
PubMed1991

Either isoform of the dopamine D2 receptor can mediate dopaminergic repression of the rat prolactin promoter.

Hypophyseal portal dopamine is a major negative regulator of pituitary prolactin (PRL) production. Dopamine has been reported to repress PRL gene transcription in pituitary cells. To facilitate further study of the effect of dopamine on PRL gene activation, we introduced PRL promoter and D2 receptor (D2R) constructs into GH3 cells. Since two D2R isoforms (termed D2S and D2L) have been cloned previously, we first determined which isoform(s) is present in the lactotroph by measuring the level of each mRNA species in rat prolactinoma. mRNA for each D2R isoform was found to be present, with the D2L mRNA in great (c. 6-fold) excess. Because the lactotroph contains both isoforms, the effect of each on the PRL promoter was investigated. The cDNA for each receptor isoform was synthesized by polymerase chain reaction, and cloned into an RSV-based expression vector. GH3 cells were then transiently co-transfected with either of the resulting RSV-D2R constructs plus a PRL-chloramphenicol acetyltransferase (CAT) construct containing the first 1957 base-pairs of PRL gene 5'-flanking DNA. The cells were then incubated 48 h plus or minus the dopamine agonist ergocryptine (ECR). In the presence of either RSV-D2R isoform, ECR yielded a 4-5-fold decrease in CAT activity, an effect not seen in the absence of the RSV-D2R. The promoter specificity of this effect was demonstrated by the inability of ECR to regulate expression of a control RSV-CAT construct. The PRL promoter repression mediated by each receptor isoform had appropriate pharmacology: the specific D2R agonist, quinpirole, yielded results similar to ECR, and the ECR repression was reversed by the dopamine antagonist spiperone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Phenylalanine uptake in neonatal and infant rat brain.

At the same severe elevations in blood phenylalanine (Phe) levels maintained for 4 h, much higher cerebral Phe concentrations were found in 4-day-old than in 16- or 70-day-old rats. In order to compare this developmental change with 14C-Phe influx mediated by the L transport system, the rapid intracarotid injection method was adapted for use in neonatal rats. The brain uptake index (BUI) thus determined for the first time through the suckling period was significantly higher on the 4th day of age than on the 7th or 24th day, while no significant change occurred during subsequent life. This early period of change in influx across the blood-brain barrier overlapped with the age period of decrease of the hyperphenylalaninemia-associated accumulation of Phe in the brain. The results indicate that by the time when intermittent feeding begins, the brain has developed a considerable ability (a) to protect itself against physiological (e.g. postprandial) fluctuations in circulating Phe levels, and (b) to restrict the cerebral accumulation of Phe from pathologically elevated blood concentrations such as those in phenylketonuria.

Animals↗
PubMed1987

Cerebral glycine content and phosphoserine phosphatase activity in hyperaminoacidemias.

Chronic hyperphenylalaninemia maintained with the aid of a suppressor of phenylalanine hydroxylase, alpha-methylphenylalanine, increases the glycine concentration and the phosphoserine phosphatase activity of the developing rat brain but not that of liver or kidney. Similar increases occur after daily injections with large doses of phenylalanine alone, while tyrosine, isoleucine, alanine, proline, and threonine, were without effect. Treatment with methionine, which increases the phosphoserine phosphatase activity of the brain and lowered that of liver and kidney, left the cerebral glycine level unchanged. When varying the degrees of gestational or early postnatal hyperphenylalaninemia, a significant linear correlation was found between the developing brains' phosphoserine phosphatase and glycine concentration. Observations on the uptake of injected glycine and its decline further indicate that coordinated rises in the brain's phosphoserine phosphatase and glycine content associated with experimental hyperphenylalaninemia denote a direct impact of phenylalanine on the intracellular pathway of glycine synthesis in immature animals.

Age Factors↗
PubMed1982

The effects of hyperphenylalaninemia on fetal development: a new animal model of maternal phenylketonuria.

A new model has been developed for the study of maternal phenylketonuria. Beginning on the 12th day of gestation the diet of pregnant rats was supplemented with 0.5% alpha-methylphenylalanine and 3% phenylalanine. This resulted in an 83% reduction of hepatic phenylalanine hydroxylase activity. The maternal plasma phenylalanine was elevated 10-20-fold for two-thirds of the day, but the degree and persistence of the fetal hyperphenylalaninemia may have been even greater. The brain phenylalanine concentrations in the fetus were raised up to 2900 nmole/g brain, whereas the highest level observed in the dam was 382 nmole/g. Experimentally-treated fetuses showed small reductions in both body and brain weight when compared to age-matched controls; however, no differences were seen in crown to rump length, litter size, DNA and protein concentrations per g, or in postnatal survival. Initiation of the diet at conception rather than on the 12th day caused a significantly greater inhibition of fetal growth, and 21% mortality. The fetal cerebral concentrations of methionine and the branched chain amino acids (valine, leucine and isoleucine) were decreased by hyperphenylalaninemia. From the 16th day on, the concentration of the inhibitor neurotransmitter glycine was elevated. Cerebral serotonin showed a 20-30% deficit and its primary metabolite 5-hydroxyindoleacetic acid a 71-77% deficit. Of twelve enzymes quantified in the brains of hyperphenylalaninemic fetuses only phosphoserine phosphatase showed any change. From the 20th to the 22nd day of gestation its activity was 46-67% higher in experimental than in normal fetuses. Measurement on the 22nd day of gestation showed that the increases in phosphoserine phosphatase activity and glycine content were present in brain stem, cerebellum, and forebrain.

Animals↗
PubMed1977

Hydroxyproline excretion following renal transplantation: comparison with values found in primary hyperparathyroidism.

The amounts of total hydroxyproline (THP), free hydroxyproline (FHP) and non-dialysable hydroxyproline (NDHP) excreted in the urine by six patients with chronic renal failure who received kidney transplants and six patients with primary hyperparathyroidism were studied. Following transplantation three of the four patients with radiological evidence of hyperparathyroidism developed hypercalcaemia and excreted more than 360 mumol THP/24 hours on at least one occasion. The remaining patients were normocalcaemic and excreted less THP and a higher proportion of NDHP. In all patients with primary hyperparathyroidism, THP excretion fell after adenoma removal but there was an increased excretion of NDHP:THP. It is suggested that studies of hydroxyproline excretion may contribute to clinical assessment of healing of renal osteodystrophy and involution of the parathyroid glands after renal allograft transplantation.

Adult↗
PubMed1977

Oestrogen-progestogen oral contraceptives and urinary calcium excretion.

To examine the effects of age and use of oestrogen-progestogen oral contraceptive agents (OCA) on urinary calcium excretion, 24 h urine collections were obtained from 525 women aged 16-69 years during a health survey, and measurements made of the amounts of calcium, creatinine, sodium, potassium and magnesium excreted. Younger women using OCA excreted more potassium and creatinine but less calcium, and less calcium and magnesium relative to creatinine, than corresponding controls using no OCA. Older women excreted less creatine, but significantly greater amounts of calcium, sodium, potassium and magnesium relative to creatinine than younger women. It is postulated that the diminished urinary calcium excretion observed in women using OCA resulted from suppression of bone resorption by oestrogens in OCA.

Adolescent↗
PubMed1976

Effects of propranolol on changes in heart rate, heart weight, kidney weight, urinary hydroxyproline and weight gain induced by large doses of thyroxine in the rat.

The effects of the beta-adrenergic receptor blocking agent, DL-propranolol, and of the antithyroid drug, carbimazole, upon some manifestations of thyroxine (T4)-induced changes in peripheral metabolism were studied in rats. Propranolol lowered the heart rate, but did not alter the following changes induced by T4: increment in heart rate, increase in heart or kidney weight, increase in urinary hydroxyproline, decrease in body weight gain or increase in serum T4. Carbimazole administration lowered serum T4 and reduced weight gain, but had no effect upon heart rate or hydroxyproline excretion.

Animals↗